Method of making composite metal body



f Dec. 12, 1933.

Xxx w A. J. LIEBMANN 1,939,628

METHOD OF MAKING COMPOSITE METAL BODY Filed March 23, 1932 Sourcefmo/rzJ/e/al Core.

Ill YEA/TOR ATTORNEYS.

W WM

Patented Dec. 12, 1933 UNITED STATES PATENT OFFICE .METHOD or MAKING COMPOSITE METAL nonr Alfred J. Liebmann,

Application March 23, 1932. Serial No. 600,641

3 Claims.

My invention relates to a new and improved method of providing a composite metal body and to a new and improved composite metal body.

One of the objects of my invention is to provide a method whereby a core of relatively cheap metal, such as iron or one of the members of the iron group, can be provided with a coating or jacket of a more expensive metal, such as copper, or the like.

Another object of my invention is to provide a method whereby a metal or alloy which is to be protected against corrosion is provided with an outer coating or covering of non-corrosive metal or alloy. l6 Another object of my invention is to provide a method whereby the outer coating or covering is firmly pressed against the interior of the core so asto eliminate any intermediate scale or air spaces. Thepresence of any such intermediate 80 scale or air spaces is objectionable, because it leads to corrosion.

Another object of my invention is to provide an article of this type in which the outer Jacket of copper or the like is subjected to an internal stress so that the inner periphery of said jacket is firmly pressed against the outer periphery of the core, said core being also maintained under interior stress.

Another object of my invention is to provide 80 an article of this type which can be rolled and otherwise mechanically worked, without any separation between the jacket and the core.

It is to be understood that my invention generally extends to any article of any kind comprising a core which is protected by an outer Jacket.

Other objects of my invention will be set forth in the following description and drawing which illustrate a preferred embodiment thereof, it be- 0 ing understood that the above general statement of the objects of my invention is intended merelyto generally explain the same and not to limit it in any manner.

In order to practice my improved method, I can utilize an ordinary crucible made of graphite or artificial graphite or any other suitable material. This crucible is preferably held in the vertical position, and the core is placed within the crucible so that the interior wall of the crucible is spaced from the exterior wall of the core. For example,

the core may be made of steel and it may be a solid core having a transverse diameter of five inches. For convenience, it can be assumed that the core is shaped like a cylinder and that the interior wall of the crucible is also of cylindrical shape. The transverse distance between the interior wall of the crucible and the exterior wall of .the core may be five-eighths of an inch, so that the improved article has a total diameter of six and a quarter inches, the core having a diameter of five inches, and the Jacket having a thickness of five-eighths of an inch. The core is held in its central position by any suitable means, and it is also prevented from moving upwardly so that the bottom of the core rests upon the bottom interior wall of the crucible.

While the core and crucible are at ordinary 1 room temperature, about F., molten copper is poured into the space between the core and the interior wall of the crucible. The copper may be poured in while it is at a temperature a little above its melting point, as for example at a temperature of about 1115 C. Since the crucible and the core are cold and since the mass of the core greatly exceeds the mass of the copper, the copper solidifies about the core. This is the preliminary step in nu improved method,

and the object is to protect the outer surface of the core from the formation of any scale. Since the molten copper comes into contact with the cold core, the copper solidifies immediately, and the core is not heated to a sufiiciently high temperature to cause the formation of oxide or scale. The crucible and its contents are then placed within a suitable furnace, such as a gas or electric furnace. The temperature of the furnace is slightly above the melting point of the metal having the lower melting point. In the example given, the copper has the lower melting point and the temperature of the furnace can therefore be about 1115' C.. The crucible and its contents are held within the furnace for a suitable period of time until the temperature of the core and of the molten copper is the same. It is particularly important to have the entire core heated to the same temperature as the molten copper. The length of the heat treatment depends largely upon the size of the core or ingot. The heat treatment may be as short as ten or 1 fifteen minutes, and it may be an hour or more.

After the metal contents of the crucible have been brought throughout to the same temperature, the crucible is then lifted out of the furnace and it is caused to cool.

I prefer to cool the crucible and its contents more rapidly than by allowing the heat of the crucible and its contents to be radiated in an ordinary room. For example, the crucible may be immersed in water or may have its exterior wall 110 is highly advantageous sprayed with water so that in the example above given, the period of cooling is about half an hour.

If the copper in the liquid state is allowed to contact with the steel during a period which is too long, there appears to be a diffusion between the copper and the steel. This is probably a diffusion of the steel into the copper. Hence, I prefer to rapidly cool the copper after the second melting thereof so as to prevent such diffusion. The diffusion of the steel into the copper lowers the electrical conductivity and I desire to minimize this.

Since the metal contents of the crucible were initially at the same temperature, previous to the cooling step, and since the core of the composite ingot has the greatest thermal capacity, and since the cooling proceeds from the outside to the inside, the copper will first solidify while the core remains relatively hot.

Copper has a greater thermal coefiicient of expansion than steel or iron. If the core would first cool and thus contract, the outer surface of the core would shrink away from the interior surface of the copper jacket. By causing the copper jacket to first solidify, the relatively thin copper jacket is caused to shrink against the relatively hot core. This produces a very firm and intimate union betwen the core and the jacket with elimination of air spaces. After the copper jacket has solidified, the core and jacket are then cooled, to ordinary room temperature, but the greater contraction of the relatively thin copper jacket causes it to shrink against the core. Hence, the completed article has the copper jacket internally stressed. The effect is the same as though a thin copper ring is heated and placed upon a core of relatively large diameter, and the thin copper ring is then allowed to cool and thus subject the core to internal pressure or stress. However, the improved method disclosed herein in that the formation of scale between the core and the jacket is elimmated. The improved ingot can be rolled and mechanically worked without any separation between the core and the jacket. The improved article of manufacture can also be recognized by the fact that there is no scale and there are no air spaces between the core and its jacket.

While I have disclosed a preferred method for making the improved article, the claims for the improved article are not to be restricted to any particular method of manufacture.

The improved method comprises welding the jacket against the core, and it will be noted that the preliminary step is to cast the jacket around the core, and to then complete and perfect the welding by subsequent heating and cooling operations.

Of course I do not wish to be limited to the use of a solid core. It is important that the jacket should be thin relative to the diameter of the core, in order to produce the shrinking effect previously mentioned.

It will be noted that a very important advantage of my invention is that I provide a body of high conductivity, such as copper, with a core of high mechanical strength, such as steel.

I do not wish to be limited to composite metal bodies which consist only of two metals. For example, the invention extends to a body com prising a steel core, a copper ring, and a steel covering. The invention extends generally to a composite metal body having any number of layers, and said layers may be made of different metals.

I have shown a preferred embodiment of my invention, but it is clear that numerous changes and omissions can be made without departing from its spirit.

I claim:

1. A method of forming a composite metal body having a metal core and a metal jacket, said core being made of material which oxidizes at the melting point of the material of said jacket, which consists in first casting the jacket around said core while keeping said core below the melting point of said jacket and below the temperature at which the periphery of said core which contacts with said jacket is caused to oxidize, and then heating said core and jacket above the melting point of said jacket so as to cause said jacket to protect the adjacent wall of the core from the formation of oxide during the fusion of said jacket, and then cooling the core and said jacket.

2. A method of forming a composite metal body having a metal core and a metal jacket, said core being made of material which oxidizes at the melting point of the material of said jacket, which consists in first casting the jacket around said core while keeping said core below the melting point of said jacket and below the temperature at which the periphery of said core which contacts with said jacket is caused to oxidize, and then heating said core and jacket above the melting point of said jacket so as to cause said jacket to protect the adjacent ,wall of the core from the formation of oxide during the fusion of said jacket, and then cooling the core and said jacket, the jacket being cooled more rapidly than the core, said jacket being made of material which has a greater thermal coefficient of shrinkage than the material of said core.

3. A method of forming a composite metal body having a ferrous core and a jacket which consists substantially of copper, which consists in pouring the molten copper around the core so that the molten copper quickly solidifies, the temperature of the core being kept sufficiently low to prevent the formation of scale thereon, and then heating the core and the jacket until the jacket melts and while the temperature of the core is kept below its melting point, and then cooling the core and its jacket, the jacket being cooled more rapidly than the core during said cooling operation, the jacket being caused to surround the adjacent wall of the core during the melting thereof.

ALFRED J. IJEBMANN. 

